Beyond the Standard model

From http://particleadventure.org/frameless/index.html

Modern physics has good theories for quantum mechanics, relativity, and gravity. But these theories do not quite work with each other. There are problems caused by our living in three spatial dimensions. If we lived in more than three dimensions, these problems would naturally resolve themselves.

String Theory, one of the recent proposals of modern physics, suggests that in a world with three ordinary dimensions and some additional very "small" dimensions, particles are strings and membranes. Yes, membranes in extra dimensions are weird and hard to visualize. And what are "small dimensions?"

While the Standard Model provides a very good description of phenomena observed by experiments, it is still an incomplete theory. The problem is that the Standard Model cannot explain why some particles exist as they do. For example, even though physicists knew the masses of all the quarks except for top quark for many years, they were simply unable to accurately predict the top quark's mass without experimental evidence because the Standard Model lacks any explanation for a possible pattern for particle masses.

Does this mean that the Standard Model is wrong?

No -- but we need to go beyond the Standard Model in the same way that Einstein's Theory of Relativity extended Newton's laws of mechanics. Isaac Newton's laws of mechanics are not wrong, per se, but his theory only works as long as velocity is much smaller than the speed of light. Einstein expanded Newtonian physics with his Theory of Relativity, which allows for the possibility of very high velocities. We will need to extend the Standard Model with something totally new in order to thoroughly explain mass, gravity and other phenomena.

I wonder what we'll decide to call the new theory that replaces the Standard Model!

The Super-Standard Model?

The New Revised Standard Model?

The Very Standard Model?

There are three "sets" of quark pairs and lepton pairs. Each "set" of these particles is called a generation, or family. The up/down quarks are first generation quarks, while the electron/electron neutrino leptons are first generation leptons.

Why are there exactly three generations of matter?

The generations increase in mass and higher generation particles tend to decay into lower generation particles. In the every-day world we observe only the first-generation particles (electrons and up/down quarks). We do not know why the natural world "needs" the two other generations, and we do not know why there are exactly three generations in total.

The Standard Model cannot explain why a particle has a certain mass. For example, both the photon and the W particle are force carrier particles: why is the photon massless and the W particle massive?

Physicists have theorized the existence of the so-called Higgs field, which in theory interacts with other particles to give them mass. The Higgs field requires a particle, the Higgs boson. The Higgs boson has not been observed, but physicists are looking for it with great enthusiasm.

Today, one of the major goals of particle physics is to unify the various fundamental forces in a Grand Unified Theory which could offer a more elegant understanding of the organization of the universe. Such a simplification of the Standard Model might well help to answer our questions and point toward future areas of study.

James Maxwell took a big step toward this goal when he unified electricity and magnetism, and physicists now understand that at high energies the electromagnetic and weak forces are aspects of the same force

Physicists hope that a Grand Unified Theory will unify the strong, weak, and electromagnetic interactions. There have been several proposed Unified Theories, but we need data to pick which, if any, of these theories describes nature.

If a Grand Unification of all the interactions is possible, then all the interactions we observe are all different aspects of the same, unified interaction. However, how can this be the case if strong and weak and electromagnetic interactions are so different in strength and effect? Strangely enough, current data and theory suggests that these varied forces merge into one force when the particles being affected are at a high enough energy.

Current work on GUT suggests the existence of another force-carrier particle that causes the proton to decay. Such decays are extremely rare; a proton's lifetime is more than 10³² years.

Some physicists attempting to unify gravity with the other fundamental forces have come to a startling prediction: every fundamental matter particle should have a massive "shadow" force carrier particle, and every force carrier should have a massive "shadow" matter particle. This relationship between matter particles and force carriers is called supersymmetry. For example, for every type of quark there may be a type of particle called a "squark."

No supersymmetric particle has yet been found, but experiments are underway at CERN and Fermilab to detect supersymmetric partner particles.

Modern physics has good theories for quantum mechanics, relativity, and gravity. But these theories do not quite work with each other. There are problems caused by our living in three spatial dimensions. If we lived in more than three dimensions, these problems would naturally resolve themselves.

String Theory, one of the recent proposals of modern physics, suggests that in a world with three ordinary dimensions and some additional very "small" dimensions, particles are strings and membranes. Yes, membranes in extra dimensions are weird and hard to visualize. And what are "small dimensions?"

String theory and other new proposals require more than three space dimensions. These extra dimensions could be very small, which is why we don't see them.

How can there be extra, smaller dimensions?

Think about an acrobat and a flea on a tight rope. The acrobat can move forward and backward along the rope. But the flea can move forward and backward as well as side to side. If the flea keeps walking to one side, it goes around the rope and winds up where it started. So the acrobat has one dimension, and the flea has two dimensions, but one of these dimensions is a small closed loop.

So the acrobat cannot detect any more than the one dimension of the rope, just as we can only see the world in three dimensions, even though it might well have many more. This is impossible to visualize, precisely because we can only visualize things in three dimensions!

Ready for a mind-boggling idea?

The majority of the universe may not be made of the same type of matter as the Earth. We infer from gravitational effects the presence of this dark matter, a type of matter that we cannot see. There is strong evidence that it might not be made up of protons, neutrons, and electrons.

What is dark matter, then? We don't know. Perhaps it is composed of neutrinos, or even more exotic forms of matter, like neutralinos, one of the theoretical supersymmetric particles